Interference effects are well founded from the quantum mechanical viewpoint and in principle cannot be ignored in realistic studies of New Physics scenarios. In this work, we investigate the size of interference effects between resonant and non-resonant contributions to di-Higgs production in the singlet extension of the Standard Model, where the additional heavy scalar provides a resonant channel. We find these interference contributions to have a non-negligible effect on the cross-sections and differential distributions. In order to allow for a computationally efficient treatment of these effects via reweighting, we introduce a new tool utilising a matrix-element reweighting method: HHReweighter. In addition to the broadly used di-Higgs invariant mass $\textit{m}$ , we analyse the sensitivity to the interference terms for other kinematic variables, such as the Higgs boson transverse momentum, and find that these also can be sensitive to interference effects. Furthermore, we provide updates on the latest experimental and theoretical limits on the parameter space of the real singlet extension of the Standard Model Higgs sector.

Germany

Finn Feuerstake

Elina Fuchs

Croatia

Tania Robens

United Kingdom

Daniel Winterbottom

Interference effects in resonant di-Higgs production at the LHC in the Higgs singlet extension

The   <math> <mi>CP</mi> </math>  $$ \mathcal{CP} $$  structure of the Higgs boson is a fundamental property which has not yet been constrained with high precision.   <math> <mi>CP</mi> </math>  $$ \mathcal{CP} $$  violation in the Yukawa coupling between the Higgs boson and top quark pair can be probed directly at the Large Hadron Collider by measuring top-quark-associated Higgs production. Multivariate analysis techniques commonly developed so far by the experiments are designed for a specific signal model and, therefore, complicate reinterpretations and statistical combinations. With this motivation in mind, we propose a   <math> <mi>CP</mi> </math>  $$ \mathcal{CP} $$ -sensitive extension of the simplified template cross-section (STXS) framework. Considering multiple Higgs decay channels, we perform an in-depth comparison of   <math> <mi>CP</mi> </math>  $$ \mathcal{CP} $$ -sensitive observables and combinations thereof. Our resulting proposal is to extend the existing binning in the transverse momentum of the Higgs boson p  T,H  by either the pseudorapidity difference of the two top-quarks   <math> <mtext>∆</mtext> <msub> <mi>η</mi> <mrow> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </mrow> </msub> </math>  $$ \Delta {\eta}_{t\overline{t}} $$ , or a variable that is based on the top quark momenta, namely b 2 or the Collins-Soper angle |cosθ ∗|. We demonstrate that this variable selection provides close to optimal sensitivity to the   <math> <mi>CP</mi> </math>  $$ \mathcal{CP} $$  mixture in the top Yukawa coupling for an integrated luminosity of 300 fb−1, by comparing it to the results of a multivariate analysis. Our results also suggest a benefit of the two-dimensional STXS extension at 3000 fb−1.

Henning Bahl

France

Alberto Carnelli

Frédéric Déliot

Anastasia Kotsokechagia

Tanguy Marsault

Marco Menen

Laurent Schoeffel

Matthias Saimpert

<math> <mi>CP</mi> </math>  $$ \mathcal{CP} $$ -sensitive simplified template cross-sections for   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>H</mi> </math>  $$ t\overline{t}H $$

High frequency gravitational waves can be detected by observing the frequency modulation they impart on photons. We discuss fundamental limitations to this method related to the fact that it is impossible to construct a perfectly rigid detector. We then propose several novel methods to search for <math><mrow><mi>O</mi><mo>(</mo><mrow><mi>MHz</mi></mrow><mo>−</mo><mrow><mi>GHz</mi></mrow><mo>)</mo></mrow></math> gravitational waves based on the frequency modulation induced in the spectrum of an intense laser beam, by applying optical frequency demodulation techniques, or by using optical atomic clock technology. We find promising sensitivities across a broad frequency range.

CERN

Norway

Torsten Bringmann

Valerie Domcke

Joachim Kopp

High-frequency gravitational wave detection via optical frequency modulation

$${\mathcal {C}}{\mathcal {P}}$$  <math> <mrow> <mi>C</mi> <mi>P</mi> </mrow> </math>   violation in the Higgs couplings to fermions is an intriguing, but not yet extensively explored possibility. We use inclusive and differential LHC Higgs boson measurements to fit the  $${\mathcal {C}}{\mathcal {P}}$$  <math> <mrow> <mi>C</mi> <mi>P</mi> </mrow> </math>   structure of the Higgs Yukawa couplings. Starting with simple effective models featuring  $${\mathcal {C}}{\mathcal {P}}$$  <math> <mrow> <mi>C</mi> <mi>P</mi> </mrow> </math>   violation in a single Higgs–fermion coupling, we probe well-motivated models with up to nine free parameters. We also investigate the complementarity of LHC constraints with the electron electric dipole moment bound, taking into account the possibility of a modified electron Yukawa coupling, and assess to which extent  $${\mathcal {C}}{\mathcal {P}}$$  <math> <mrow> <mi>C</mi> <mi>P</mi> </mrow> </math>   violation in the Higgs–fermion couplings can contribute to the observed baryon asymmetry of the universe. Even after including the recent analysis of angular correlations in  $$H\rightarrow \tau ^+\tau ^-$$  <math> <mrow> <mi>H</mi> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msup> <mi>τ</mi> <mo>-</mo> </msup> </mrow> </math>   decays, we find that a complex tau Yukawa coupling alone may be able to account for the observed baryon asymmetry, but with large uncertainties in the baryogenesis calculation. A combination of complex top and bottom quark Yukawa couplings yields a result four times larger than the sum of their separate contributions, but remains insufficient to account for the observed baryon asymmetry.

United States

Spain

Sven Heinemeyer

Judith Katzy

Krisztian Peters

Georg Weiglein

Constraining the  $${\mathcal {C}}{\mathcal {P}}$$  <math> <mrow> <mi>C</mi> <mi>P</mi> </mrow> </math>   structure of Higgs-fermion couplings with a global LHC fit, the electron EDM and baryogenesis

We develop an efficient method for solving transport equations, particularly in the context of electroweak baryogenesis. It provides fully-analytical results under mild approximations and can also test semi-analytical results, which are applicable in more general cases. Key elements of our method include the reduction of the second-order differential equations to first order, representing the set of coupled equations as a block matrix of the particle densities and their derivatives, identification of zero modes, and block decomposition of the matrix. We apply our method to calculate the baryon asymmetry of the Universe (BAU) in a Standard Model effective field theory framework of complex Yukawa couplings to determine the sensitivity of the resulting BAU to modifications of various model parameters and rates, and to estimate the effect of the commonly-used thin-wall approximation.

Israel

United Arab Emirates

Marta Losada

Yosef Nir

Yehonatan Viernik

Analytic techniques for solving the transport equations in electroweak baryogenesis

Spin-0 singlets arise in well-motivated extensions of the Standard Model. Their lifetime determines the best search strategies at hadron and lepton colliders. To cover a large range of singlet decay lengths, we investigate bounds from Higgs decays into a pair of singlets, considering signatures of invisible decays, displaced and delayed jets, and coupling fits of untagged decays. We examine the generic scalar singlet and the relaxion, and derive a matching as well as qualitative differences between them. For each model, we discuss its natural parameter space and the searches probing it.

Oleksii Matsedonskyi

Inbar Savoray

Matthias Schlaffer

Collider searches for scalar singlets across lifetimes

We explore the implications of the Standard Model effective field theory (SMEFT) with dimension-six terms involving the Higgs boson and third-generation fermion fields on the rate of Higgs boson production and decay into fermions, on the electric dipole moments (EDMs) of the electron, and on the baryon asymmetry of the Universe. We study the consequences of allowing these additional terms for each flavor separately and for combinations of two flavors. We find that a complex Yukawa coupling can account for the observed baryon asymmetry $$ {Y}_B^{\mathrm{obs}} $$ within current LHC and EDM bounds. A complex ( ) Yukawa coupling can account for 4% (2%) of $$ {Y}_B^{\mathrm{obs}} $$ , whereas a combination of the two can reach 12%. Combining with either or enlarges the viable parameter space owing to cancellations in the EDM and in either Higgs production times decay or the total Higgs width, respectively. Interestingly, in such a scenario there exists a region in parameter space where the SMEFT contributions to the electron EDM cancel and collider signal strengths are precisely SM-like, while producing sufficient baryon asymmetry. Measuring violation in Higgs decays to leptons is the smoking gun for this scenario.

C P violation from τ , t and b dimension-6 Yukawa couplings — interplay of baryogenesis, EDM and Higgs physics

The upper bounds from the ATLAS and CMS experiments on the decay rate of the Higgs boson to two muons provide the strongest constraint on an imaginary part of the muon Yukawa coupling. This bound is more than an order of magnitude stronger than bounds from <math><mi>C</mi><mi>P</mi></math>-violating observables, specifically the electric dipole moment of the electron. It excludes a scenario—which had been viable prior to these measurements—that a complex muon Yukawa coupling is the dominant source of the baryon asymmetry. Even with this bound, the muon source can still contribute <math><mi>O</mi><mo>(</mo><mn>16</mn><mo>%</mo><mo>)</mo></math> of the asymmetry.

Implications of the Upper Bound on <math><mi>h</mi><mo>→</mo><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math> on the Baryon Asymmetry of the Universe

We propose six new benchmark scenarios for Higgs boson searches in the Minimal Supersymmetric Standard Model. Our calculations follow the recommendations of the LHC Higgs Cross Section Working Group, and benefit from recent developments in the predictions for the Higgs-boson masses and mixing. All of the proposed scenarios are compatible with the most recent results from Run 2 of the LHC. In particular, they feature a scalar with mass and couplings compatible with those of the observed Higgs boson, and a significant portion of their parameter space is allowed by the limits from the searches for SUSY particles and additional Higgs bosons. We define a scenario where all SUSY particles are relatively heavy, and two scenarios with light colorless SUSY particles (charginos, neutralinos and, in one case, staus). In addition, we present two scenarios featuring alignment without decoupling, realized with either the lighter or the heavier scalar being SM-like, and a scenario with $$\mathcal {CP}$$ <math><mi>CP</mi></math>  violation.

Switzerland

Emanuele Bagnaschi

Thomas Hahn

Stefan Liebler

Shruti Patel

Pietro Slavich

Tim Stefaniak

Carlos Wagner

MSSM Higgs boson searches at the LHC: benchmark scenarios for Run 2 and beyond

We study the potential of future lepton colliders, running at the Z-pole and above, and the High-Luminosity LHC to search for the relaxion and other light scalars ϕ. We investigate the interplay of direct searches and precision observables for both   <math> <mi>C</mi> <mi>P</mi> </math>  $$ \mathcal{C}\mathcal{P} $$ -even and -odd couplings. In particular, precision measurements of exotic Z-decays, Higgs couplings, the exotic Higgs decay into a relaxion pair and associated Zϕ and γϕ production are promising channels to yield strong bounds.

Claudia Frugiuele

Gilad Perez

Relaxion and light (pseudo)scalars at the HL-LHC and lepton colliders